Hello. I've been working on photosynthesis pigment content in in vitro grown trees and was examining the formulas for determining the concentration of chlorophyll a and b and carotenoids based on absorbance, i.e. using a spectrophotometer. I've found various formulas, and even though they all share the same general design: concentration=coefficient1*adsorbance1-coeficeint2*adsorbance2, the coefficients differ among sources. I was curious as to the reason behind this. Is it due to the use of different equipment, i.e. every spectrophotometer is different, or something else? I'm new to this field, thus any help, directions to relevant introductory literature, articles, would be great.
Hi,
The reason for the different coefficients could be that different solvents were used or the coefficients are for different wavelengths.
Another reason could be "historic" coefficients, which were at the time they were published state of the art, but are now outdated by more accurate coefficients. For chlorophylls, you can find a discussion here: https://link.springer.com/article/10.1007%2Fs11120-018-0579-8
Philipp Girr Thanks. This was very helpful. Maybe you could help me with another question. Why does this general formula (concentration=coefficient1*adsorbance1-coeficeint2*adsorbance2) carries the values of µg/ml or mg/ml? Even in the article you suggested, they mention that they simply multiplied the number they got by a 1000, and got µg/ml?
The factor 1000 converts the output of the formula from µg/l to µg/ml or from mg/l to mg/ml. These are the standard units for pigment concentration. In the end, it doesn't matter too much which unit you use because you can easily convert it into other units and since we also know molecular weights you could even convert into molar concentrations.